Environmental fluid dynamics of tidal bores: Theoretical considerations and field observations
A tidal bore is a series of waves propagating upstream as the tidal flow turns to rising in a river mouth during the early flood tide. The formation of the bore occurs is linked with a macro-tidal range exceeding 4.5 to 6 m, a funnel shape of the river mouth and estuarine zone to amplify the tidal range. After formation of the bore, there is an abrupt rise in water depth at the bore front associated with a flow singularity in terms of water elevation, and pressure and velocity fields. The application of continuity and momentum principles gives a complete solution of the ratio of the conjugate cross-section areas as a function of the upstream Froude number. The effects of the flow resistance are observed to decrease the ratio of conjugate depths for a given Froude number. The field observations show that the tidal bore passage is associated with large fluctuations in water depth and instantaneous velocity components associated with intense turbulent mixing. The interactions between tidal bores and human society are complex.A tidal bore impacts on a range of socio-economic resources, encompassing the sedimentation of the upper estuary, the impact on the reproduction and development of native fish species, and the sustainability of unique eco-systems. It can be a major tourism attraction like in North America, Far East Asia and Europe, and a number of bores are surfed with tidal bore surfing competitions and festivals. But a tidal bore is a massive hydrodynamic shock which might become dangerous and hinder the local traffic and economical development.